This invention relates to control systems for slide centrifuges and more particularly to methods of and apparatus for producing blood smeared slides for clinical analysis.
Examination of cell morphology yields important medical data. Frequently, cell samples are obtained in the form of cells suspended in a liquid. A particular case is the analysis of blood samples. The blood is smeared on a laboratory slide and the smear is stained. By counting the leukocytes on the stained smear, laboratory technicians perform what is referred to as a white blood cell differential count. Recently, the analysis of blood smeared slides has been automated. In automated analysis, it is particularly important to consistently produce a slide with a uniform monolayer of blood cells.
U.S. Pat. No. 3,577,267 Preston et al. and U.S. Pat. No. 3,705,048 Staunton describe centrifuges which can be used to prepare blood slides. However, the problem is that the spinning time must be changed for different blood smears because blood of different hematocrits and other blood properties requires different spinning times to produce a uniform monolayer.
One solution to this problem is disclosed in U.S. Pat. No. 3,827,805, Mansfield et al wherein the time of spinning is controlled by a signal derived from photodetectors which detect the ratio of direct and scattered light passing through the spinning slide. This control arrangement does not directly measure the separation of the cells. Occasionally, the optical and physical properties of the blood are such as to cause unduly short or unduly long spin times, causing slides to be under or overspun. Moreover, it is sometimes difficult to align the optical systems which detect the ratio of direct and scattered light.